Because microfabrication by top-down approach is physically limited (by the wavelength of laser beam), one-dimensional nanoscale microstructures are expected to play an important role for electronic devices. Intensive research and development works are going on in this field.
Among typical topics of such research are carbon nanotube (CNT) and metal nanowire. These materials, however, are hard to handle because of their small size. Their practical use will be feasible only after 2010 on account of problems with assembling and integration.
Active researches are going on for the method of their synthesis with a high degree of orientation. The resulting materials are expected to find use in field emission display and memory. There has been proposed a method of producing CNT by vapor phase growth in pores in zeolite or anodized alumina with pores functioning as a template. This method has been reported to be successful in synthesis of highly oriented CNT. (See Non-Patent Document 1.)
On the other hand, the method for grinding a material by using a focused ion beam (FIB), which is intended to thin a sample or skive a surface, is mainly used to prepare samples for observation under an electron microscope. (See Patent Document 1.) FIB has the advantage of being capable of performing sputtering on any material and grinding selectively a very small region (depending on the beams's spot size), without surface oxidation which is encountered in chemical methods.
A new method has been disclosed which consists of depositing three-dimensional microstructures by irradiation with FIB in a gaseous atmosphere. (See Patent Document 2.)
However, the use of FIB disclosed in the past is nothing more than energy irradiation.
Non-Patent Document 1: Uung Sang Suh, Applied Physics Letters 75, 2047 (1999) p. 2047, from line 32 in left column to line 15 in right column)
Patent Document 1: Japanese Patent Laid-open No. Hei 4-361132 (lines 24 to 49 in the second column; FIG. 1)
Patent Document 2: Japanese Patent Laid-open No. 2001-107252 (lines 32 to 45 in the fourth column; FIG. 1)
The related art technologies mentioned above, however, suffer the following disadvantages. Making pores in alumina by anodic oxidation (which is a chemical process) presents difficulties with controlling the pore diameter and avoiding the entrance of impurities during chemical reactions.
Moreover, CNT synthesized in pores made by anodic oxidation has a limited diameter that depends on the diameter of the pore as a template. The smallest diameter that can be achieved at the present time is about 80 nm, and a further reduction is required. Another disadvantage of this process is that the resulting CNT has a low degree of crystallinity in its wall structure and hence it does not exhibit ballistic conduction as a merit of CNT.
The present invention was completed to address the above-mentioned problems. It is an object of the present invention to provide a method of producing microstructure and a method of producing mold, the methods permitting production of much smaller pores than before in an atmosphere where impurities are negligible and also permitting production of microstructures having a smaller size and a higher crystallinity than before with the help of the pores.